I'm wanting to know which "stationary" len would be the best to capture up to a 40" x 30" piece of art (the smallest would 18" x 14") without any "keystoning" at a distance of 10 feet. I'm looking to build my own "large" digital format scanner/capture system - Any suggestions or information would be appreciated.

Do you have a camera system in mind as the lens choice will depend on that.

To photograph a 40x30 inch item completely from 10 feet would take around 90mm on full frame DSLR, or 60mm on a crop sensor DSLR. These values are rounded down to nearest common focal length. For smaller items you'd have to get closer or use a different lens.

Keystoning, if its what I think you're talking about, is primarily an effect of the camera position, not the lens. As long as the camera sensor is placed parallel to the subject, then there wont be significant perspective distortion.

With the camera sensor parallel to the subject, then to best fill it, you'd have to be central to the target. In case you absolutely need to be off centre, then a tilt shift lens be able to correct for that. This can be handy if the subject is highly reflective and you don't want the camera in the reflection.

The old saying "you get what you pay for" comes in here I think. Assuming the large format scanner runs at 600 dpi, you're looking at output resolutions of 36000x24000 for the 60x40. Taking the relatively affordable higher resolution full frame Canon 5D mk2, it outputs at 5616 x 3744. The scanner output would be about 41x the size in area! So the question then is what level of quality do you really need? There are higher resolution photographic options but again the cost is increasing significantly at that point.

Art galleries must tackle this issue all the time.Photo's of works of art are normally seen all over the place.

One of the things to check is the software that can link with the camera. Canon for instance has the EOS utility which can connect to the camera and control it from the software on the computer.

For a true 'scan' type image there will be a need for optical correction, the longer the focal length of the lens the less correction is needed. I'm pretty sure the Canon software (Digital Photo Professional) that comes on a disk with a camera, will correct both distortion and vignetting.

As well as the camera working out a good workflow will help the resulting image accuracy.